In an effort to meet emissions standards, various sensors may be included in an engine exhaust system to estimate tailpipe emissions and/or enable accurate control over various exhaust emission control devices. Accurate measurement of exhaust gas compounds may enhance the operation of exhaust treatment systems, such as Selective Catalytic Reduction (SCR) units, as well as enable accurate air-fuel ratio feedback control. However, accurate sensor readings assume an even distribution of compounds in an exhaust stream in order to use a sampled measurement to be extrapolated to the compound concentrations in the full stream. Exhaust as in the exhaust manifold or immediately downstream of the exhaust manifold may include a non-homogeneous mixture of constituents due to the pulsed nature of the release of exhaust gas from each cylinder. For example, the exhaust gas from a given cylinder may not adequately mix with exhaust gas from another cylinder until each respective exhaust gas stream has traveled relatively far down the exhaust passage. As different cylinders may experience different combustion conditions (e.g., different fuel injection amounts, ignition timing, cylinder pressures, etc.), exhaust constituents may not be evenly distributed throughout the exhaust manifold and/or exhaust passage. Consequently, there may be a discrepancy between the concentration of an exhaust gas constituent as estimated by a sensor in the exhaust, and the concentration of the constituent in the bulk exhaust gas, particularly when the exhaust sensor is positioned in a close-coupled position to the exhaust manifold. Thus, the accuracy of the sensor may be degraded, leading to degraded engine emissions.
Attempts to address the problem of homogenous gas mixing in the exhaust passage of an engine include placing static flow mixers in the exhaust passage, an example of which is shown in US 2014/0133268. Therein, an annular support with radial vanes converging towards a center opening introduces a swirl in the exhaust gas, promoting mixing of exhaust gas with injected reductant while minimizing backpressure via the center opening.
However, the inventors herein have recognized potential issues with such systems. As one example, localized pockets of unmixed exhaust gas may persist downstream of the mixer, due to the center opening and mixing of exhaust gas in only one direction. Thus, the exhaust may not be homogenous for accurate sensor output.
To mitigate the problem of poor mixing of exhaust gas in an exhaust passage, the inventors herein describe a static flow mixer including a plurality of open channels coupled to a central support structure, each open channel of the plurality of open channels having a head bending in a first direction along a longitudinal axis, a tail bending in a second direction along the longitudinal axis, and set of lobes at the tail.
In one embodiment, the plurality of open channels may include at least one diverge channel and least one converge channel. Bends in the converge channels and in the diverge channels may create a flow path that moves exhaust gas from one plane of the exhaust passage to a second plane of the exhaust passage, such as from the peripheral area to the center area of the exhaust passage and vice versa.
In this way, the open converging channels and the open diverging channels coupled to a central support may improve gas flow mixing by moving the gas from the center of the exhaust passage to the periphery of the exhaust passage through the diverge channels, and by moving the gas from the periphery to the center of the exhaust passage through the converge channels. Additionally, the converge channels and diverge channels may include lobes at the channel tail, which may direct the exhaust gas exiting the tail of the channels in a clockwise and counter-clockwise direction, resulting in a more homogenous gas mix and increasing accuracy of sensor output.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.